1. Field of the Invention
This invention is directed to an improved cage assembly for impact mills to obtain the fan effect of the mill rotor in assuring down draft operation.
2. Description of the Prior Art
The normal construction by almost all manufacturers of impact shredders or hammer mills has provided a type of cage design in which the cage is made up of a grate consisting of a series of separate ribs supported at the opposite ends. Examples are seen in 3,610,543 of Oct. 5, 1971, 3,806,048 of April 23, 1974 or 4,009,836 of Mar. 1, 1977. The ribs usually present a series of spaces having a dimension about equal to the thickness of the grate to make up a strong, rigid and substantially unbending cage over the outlet of the mill. The spaces or openings in the grate are aligned to be oriented along radii from the axis of the hammer rotor.
It was heretofore believed that the cage had to be rigid and that the outlet through the grate should be divided into narrow passages in order to size the particles that could pass through. The result of that typical grate structure was that the high differential pressure across the grate, and the resistance to the flow of air created a back flow toward the incoming supply of material due to the lift of the rotating hammers, and any light weight materials, like paper, plastic scraps, were blown up through the inlet to create a mess around the inlet to the mill. When the reverse flow which created the mess was not desired, a suction fan connected to the mill outlet had to be used.